After losing the game, press Left at the "Continue" screen to enter a hidden room that contains four extra lives.

When you begin on the main screen after choosing "Start", go to the upper left-hand corner. You will see some trees. Go left into the top ones and then press [Up]. Note: If it does not work, press [Left] more, then try it again). This should lead you to a hidden room with only one readable grave with death hovering over the top of it.